DESCRIPTION (Adapted from Applicant's Description): This proposal focusses on using Magnetic Resonance (MR) imaging to study injury induced joint degeneration and subsequent repair mechanisms and the manifested changes in articular cartilage, subchondral bone and peri-articular trabecular bone. It aims to establish the relative role and interaction between cartilage and bone changes in injury induced osteoarthrosis (OA). Osteoarthrosis, often caused by injuries to the knee joint, alters mechanical joint loading, and all the major joint tissues, including the articular cartilage, synovium, subchondral and trabecular bone and muscle have been implicated. The condition is characterized by a long asymptomatic phase when articular cartilage degenerates, reparative changes occur and radiographic changes develop. A symptomatic or painful stage then develops after irreversible cartilage damage has occurred and radiographic changes progress. It has been hypothesized that articular degeneration and progression of OA may be preceded by changes in subchondral and trabecular bone. Although trabecular bone interactions are implicated in early OA, the changes in the trabecular bone adjoining the articular cartilage associated with OA, are unclear and the trend of changes has not been defined conclusively. In this context, magnetic resonance imaging (MR), which has recently been used to depict trabecular bone structure may potentially be a valuable tool, particularly since MR images may also be used to quantify the cartilage volume, thickness, water diffusion and relaxation time which characterize the biochemical status of the cartilage, as well as measure trabecular bone. The investigators propose to make use of recent advances in MR to accurately quantify (1) the 3-D morphology and relaxation time and water diffusion characteristics of articular cartilage, and (2) the 3-D architecture of the trabecular bone network adjoining the articular cartilage, subchondral bone thickness, and density in normal and osteoarthritic (mild and severe or Kellgren-Lawrence scale 1 and 4) subjects. They aim to derive the relation of these measures to clinical measures such as pain and disability (WOMAC scale, Health Activity Questionnaire, etc.) and radiographic evidence of osteoarthrosis as demonstrated by Kellgren-Lawrence Scores. Subjects with mild OA and normals will also be followed longitudinally to determine the progression of joint degeneration, the relative chronological occurrence of bone and cartilage changes, and the ability of MR to predict joint degeneration and reflect the repair mechanisms postinjury.